1.FINISHES TO IMPROVE THE WET FASTNESS Presented By Muhammad Moosa Abdul Rehman, SDC BS, MS Textiles (III), ITRC Indus University Edited By Muhammad Awais Imran, SDC BS, MS Textiles(III), ITRC Indus University

2. INTRODUCTION Chemical finishing is defined as and includes all processes after coloration that provides better properties and that enable the qualified use of the treated textiles. But dyers and printers are often responsible for finishes that improve colour fastness. Nowadays coloured textiles have to fulfill many requirements. Therefore improvement in the colour fastness is a type of chemical finishing of particular practical interest and importance 3. DEFINITIONS & TERMS Colour fastness is the resistance of a material to change in any of its colour characteristics, to the transfer of its colourants to adjacent materials or both. Fading means that the colour changes and lightens. Bleeding is the transfer of colour to a secondary, accompanying fibre material. This is often expressed as soiling or staining meaning that the accompanying material gets soiled or stained 4. FASTNESSES RATING Generally fastness properties are expressed in ratings of fastness. These fastnesses ratings are normally evaluated by the grey scales for bleeding and for fading. They consist of five different grey colour gradations and are compared with the tested textile and its prescribed adjacent material. 5 = Best/Excellent 4 = Better 3 = Average 2 = Poor 1 = Very Poor 5. FASTNESSES RATING Only the light fastness ratings range up to eight for the best behavior. They are mostly evaluated on the so-called blue scales. These contain stripes of standard dyeings on wool with eight blue dyestuffs that have different light. 6. HOW TO IMPROVE WET FASTNESS? The physical and chemical principles involved in the performance of the fastness improving finishes concern either the interaction with the dyestuff or with the fibre or both. The simplest after treatment to achieve better wet fastness can be an intensive washing process. Thus wool dyeings are washed under mild alkaline conditions with ammonia, soda or sodium hydrogen carbonate. Here, Some approaches are discussed, 7. CELLULOSIC TEXTILES Cellulose fabrics dyed or printed with reactive dyestuffs are washed at high temperature often with special auxiliaries that have dispersing, sequestrating and dissolving (hydration, increased solubility) properties. Compounds with a high affinity for reactive dyes, or more precisely for their hydrolysates are helpful, the so-called colour transfer inhibitors, for example polyacrylic acid derivative 8. CELLULOSIC TEXTILES Another approach for removing reactive dye hydrolysates from the fibre and from the wash water (decolourised waste water) is the use of peroxidases (oxidative active enzymes such as Baylase RP). This multipurpose enzymatic rinse process saves time, energy and water but it is restricted mainly to jet applications. The question of the potential toxicity of the resulting aromatic nitro-compounds (cleavage products of the reactive azoic dyes) has to be resolved 9. SYNTHETIC TEXTILES When polyester textiles are deeply dyed they need an after treatment with reductive agents to remove and destroy the unfixed or only weakly fixed disperse dyestuffs on the fibre surface (reductive decomposition). With these after washings or after cleanings the colour fastness can be elevated up about one rating. 10. WET FASTNESS The widespread principle that enables the wet fastness of dyeings to be improved with anionic dyestuffs (such as reactive, direct and acid dyes) is their molecule enlargement. It causes reduced water solubility, generated by dyesalt formation of the anionic dyestuffs in the fibre with the cationic products applied after dyeing (Fig. 1). For lesser requirements, enclosure of the dyestuffs in cellulose fibres 11. AUXILIARIES Fig 1 12. ANOTHER APPROACH Another solution to the problem is the reactant fixation of the dyestuffs to the fibre with highly reactive uncoloured chemicals. Their main problem is their essential high reactivity, which causes cancer or mutagenicity when they come into contact with the finish workers. The end user is not involved because after the fixation reaction these chemicals lose their risk to health 13. APPLIED CHEMISTRY An older method of improving the wet fastness of selected direct dyeings is their diazotisation on the fibre, followed by the reaction with so-called developers (coupling compounds). The great effort and handling problems involved have made this method unattractive. 14. CATIONIC PRODUCTS Cationic products, for example polyammonium compounds, the so- called polyquats are shown in Fig. 1. Many successful products are based on quater-nary polyheterocycles such as polydiallyldimethyl ammonium chloride (DADMAC). They are mostly used for direct and reactive dyed cellulose and improve the wet fastness for about one to, at most, two ratings. The washing fastness is usually more improved than the contact fastness (water or perspiration fastness). Quaternary ammonium polymers are often used to shorten the long washing processes (soaping at the boil) of reactive dyes on cellulosics, thus providing relatively good wet fastness. 15. ISSUES WITH CATIONS Their high affinity for cellulose enables exhaust application. But cationic products can cause several problems: Insufficient permanence of the effects of repeated washings, caused by salt formation with anionic surfactants and release of the immobilised dyestuff Variation of the degree of wet fastness improvement, depending on the specific dyestuff interaction Reduced light fastness and colour changes, which are also dyestuff specific Competition with cationic soft handle products (blocking their uptake) Greying and increased soiling when applied in large amounts (cationised cotton) Stripping off is only possible with large amounts of anionic surfactants Fish toxicity, almost no biodegradation but high rate of elimination in the waste water. 16. FORMALDEHYDE PRODUCTS Formaldehyde condensation products from urea and/or melamine are shown in Fig.2. They are comparable to the corresponding products for permanent press and easy-care finishes . They have the same advantages and disadvantages and they often improve the perspiration more than the washing fastness. Therefore they are mostly used for lining fabrics, where their price advantage is especially important 17. Fig. 2 Precursor of the formaldehyde condensation polymer that improves wet fastness on cellulosic fabrics. 18. ISSUES Some possible disadvantages are: Harsher handle (requiring combination with softeners) Decreased light fastness up to two ratings (a problem more for reactive dyed fabrics than for direct dyed ones, the latter often provide greater light fastness) Colour changes (the dyer has to take these into consideration during the dye recipe formulation) Formaldehyde release. 19. AROMATIC SULPHONIC ACIDS The condensation products of aromatic sulfonic acids are used for dyeing and printings on nylon fibres, especially for the after treatment of carpets, to improve their wet fastness by up to about two ratings. Their common name is syntan, derived from synthetic tannin. Figure .3 shows typical structures of syntans (partly from Brennich and Engelhardt). These formaldehyde condensation prod-ucts of sulfonated phenols and naphthalenes are also used as reservation agents for dyeing fibre blends and as stain blockers 20. Fig .3: Reaction products of formaldehyde and aromatic sulfonic acids (syntans) improve wet fastness on nylon. 21. HOW IT WORKS? Formaldehyde connects the aromatic rings in the form of relatively stable methylene bridges. Therefore release of formaldehyde from these finishes is very low. The preferred application of anionic syntans to nylon is by exhaustion at 70 80 C and pH 3.55. They form a barrier near the fibre surface to the anionic dyes in the fibre, mainly caused by anionic repulsion. 22. HOW IT WORKS? Another theory favours the aromatic attraction of dyestuff and syntan, thus hindering the dyestuff molecules from migrating out of the fibre. The disadvantages of classical syntans are reduced bath stability and decreased efficiency caused by pseudocationic surfactants, for example, levelling agents based on fatty amine ethoxylates. Newly developed syntans have decreased these problems and can be used in the exhausted dye bath instead of fresh finishing solutions 23. REACTIVE COMPOUNDS Epoxy derivatives with cationic structures (Fig.4) have been and are still used as reactive fixation compounds. Under alkaline application conditions the epichlorohydrin groups generate very reactive epoxy ring structures that provide stable ether bondings to the hydroxyl groups of the cellulose fibre (Fig.5). 24. Thus the cationic groups are permanently fixed and attract the anionic dyestuff very effectively with astonishingly high fastness ratings for selected direct dyestuffs of up to 45 for washing at 95 C. If lower wet fastness is accepted, reduced amounts of fixation agents enable controlled fastness ratings. Apart from the health problems already mentioned during handling and application, there are other disadvantages The fixation agent can only be applied by padding and the high permanence causes problems with the correction of the shade after imperfect dyeing. 25. Fig. 4: Reactive fixatives for anionic dyes on cellulose. 26. Fig. 5: Reactions of cellulose reactive fixatives. 27. EVALUATION METHOD Standard procedures for colour fastness and especially wet fastness evaluations (for example ISO, AATCC, ASTM, BS, DIN, FTMS, Marks & Spencer) are used to evaluate the treated and accompanying fabrics. 28. TROUBLESHOOTING Some potential problems with finishes designed to improve wet fastness include: Levelness when applied on packages (crosswound bobbins) Less absorbency caused by some products Low durability of the effects in use, for example after several washings, especially with formaldehyde condensation or non-fibre reactive cationic prod-ucts (salt exchange processes with anionic surfactants). 29. CLARIANTS PRODUCTS (CATIONIC) 30. AUXICOLORS INNOVATIVE PRODUCT Polycarboxylate Polymers It is an anionic in nature Improve the wet fastness properties without changing shade (Clariants product changes the shade) Have multiple applications in: Direct, Reactive, vat & sulphur dyes 31. THANKS READINGMATERIALS 1. http://www.siampro.net/index.php?option=com_content&view=article&id=85 2. Clariant Website: Fixing Agents for Reactive Dyeing 3. Chemical Finishing of Textiles, Woodhead publishing 4. Cellulosic Dyeing, John Shore, SDC 5. Wet Processing of Cellulosic Textiles, Dr. Ahmad Niaz 6. Critical Solutions in the Dyeing of Cotton Textile Materials by Dr. Tanveer Hussain (Books are available on ITRC Site Books Section)